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4 Multi-touch (MT) Protocol
7 :Copyright: |copy| 2009-2010 Henrik Rydberg <rydberg@euromail.se>
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13 In order to utilize the full power of the new multi-touch and multi-user
16 document describes the multi-touch (MT) protocol which allows kernel
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34 packet. Since these events are ignored by current single-touch (ST)
39 input_mt_sync() at the end of each packet. This generates a SYN_MT_REPORT
48 All drivers mark the end of a multi-touch transfer by calling the usual
62 important. Event filtering and finger tracking is left to user space [#f3]_.
67 the ABS_MT_TRACKING_ID of the associated slot. A non-negative tracking id
68 is interpreted as a contact, and the value -1 denotes an unused slot. A
72 end. Upon receiving an MT event, one simply updates the appropriate
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95 Here is what a minimal event sequence for a two-contact touch would look
124 last SYN_REPORT will be dropped by the input core, resulting in no
125 zero-contact event reaching userland.
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131 Here is what a minimal event sequence for a two-contact touch would look
152 ABS_MT_TRACKING_ID -1
162 ABS_MT_TRACKING_ID -1
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186 than unity, is related to the contact pressure. For pressure-based devices,
217 direction of the finger ellipse is given by the vector (a - b).
227 implicitly handled by input core; drivers should instead call
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260 of TOUCH and WIDTH for pressure-based devices or any device with a spatial
273 turned to the left, and a positive value when the ellipse is turned to the
276 direction, the range -max should be returned.
280 indicate more than a quarter of a revolution. For an upside-down finger,
315 For type B devices, this event is handled by input core; drivers should
323 the contact. This is a low-level anonymous grouping for type A devices, and
324 should not be confused with the high-level trackingID [#f5]_. Most type A
331 time. For type B devices, this event is handled by input core; drivers
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374 ellipse should align with the vector (T - C), so the diameter must
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402 in a finger packet must not be recognized as single-touch events.
404 For type A devices, all finger data bypasses input filtering, since
407 .. [#f1] Also, the difference (TOOL_X - POSITION_X) can be used to model tilt.